Lateral raise machines offer a viable alternative to doing lateral or side raises with dumbbells. Using a machine instead of dumbbells means you'll get plenty of lumbar support from the back rest of the machine; many machines have off-center cams so that the resistance is optimized as you raise your arms. This is in contrast to the dumbbell version which gets harder as you lift the weights away from your body. Machine laterals and dumbbell laterals work the same muscles.

Dynamic Deltoids

The main muscle or agonist in machine lateral raises is your medial or lateral deltoids which are one of three deltoid or shoulder muscles. Your medial deltoids are located on the outside of your shoulders and are responsible for shoulder joint abduction -- the action of lifting your arms away from your sides. Making these muscles bigger will make your shoulders wider.

Super Supraspinatus

Located deep in your shoulder and part of your rotator cuff, the supraspinatus muscle initiates shoulder abduction. That is to say, it kick-starts the lateral raise movement and then your larger and more powerful deltoids take over. Because this muscle is comparatively weak, it is easily injured so always start each repetition of lateral raises with a smooth lift-off rather than a jerk.

Terrific Trapezius

As your upper arms approach parallel to the floor, your shoulders stop abducting and your shoulder girdle moves into elevation. This simply means that your shoulders shrug upward at the top of the lateral raise movement. Elevating your shoulders is the job of your upper trapezius muscles. If you keep your shoulders down, this muscle is less involved in this exercise but will still be working as a shoulder girdle stabilizer. Your upper trapezius is located on your upper back and across the back of your shoulders.

Synergists Galore

Your anterior deltoids, supraspinatus and upper trapezius are arguably the most active muscles in side lateral raises but there are also several other noteworthy if less well-known muscles involved. These muscles are commonly called synergists. Serratus anterior works hard to keep your scapula flat against your ribs while your middle and lower trapezius work to stabilize your shoulder girdle. Levator scapula, which works alongside your upper trapezius, helps lift your shoulders at the top of the movement and even your arm muscles get in on the act, albeit indirectly.

About the Author

Patrick Dale is an experienced writer who has written for a plethora of international publications. A lecturer and trainer of trainers, he is a contributor to "Ultra-FIT" magazine and has been involved in fitness for more than 22 years. He authored the books "Military Fitness", "Live Long, Live Strong" and "No Gym? No Problem!" and served in the Royal Marines for five years.